What is shell molding? What does the shell molding mean?

What is shell molding?

Shell molding, also known as shell mold casting or the Corroning process, is a form of metal casting dating back to the middle of the 20th century.

The metals of shell mold casting are most commonly using cast iron, carbon steel, alloy steel, stainless steel, aluminum alloys, and copper alloys. A sizable amount of the casting in the steel industry are made by shell molding process, that ensures better profitability. Typical parts manufactured in industry using the shell mold casting process include cylinder heads, gears, bushings, connecting rods, camshafts and valve bodies.

The process of creating a shell mold consists of six steps:

1.Fine silica sand that is covered in a thin (3–6%) thermosetting phenolic resin and liquid catalyst is dumped, blown, or shot onto a hot pattern. The pattern is usually made from cast iron and is heated to 230 to 315 °C (450 to 600 °F). The sand is allowed to sit on the pattern for a few minutes to allow the sand to partially cure.

2.The pattern and sand are then inverted so the excess sand drops free of the pattern, leaving just the "shell". Depending on the time and temperature of the pattern the thickness of the shell is 10 to 20 mm (0.4 to 0.8 in).

3.The pattern and shell together are placed in an oven to finish curing the sand. The shell now has a tensile strength of 350 to 450 psi (2.4 to 3.1 MPa).

4.The hardened shell is then stripped from the pattern.

5.Two or more shells are then combined, via clamping or gluing using a thermoset adhesive, to form a mold. This finished mold can then be used immediately or stored almost indefinitely.

6.For casting the shell mold is placed inside a flask and surrounded with shot, sand, or gravel to reinforce the shell.

Shell Molding Casting Advantages:

One benefit of the shell molding process, compared with other metal casting techniques, is that castings produced this way often require minimal finishing. The use of a core in shell molding replaces machining in many cases, and the surface finish achieved with shell molding is already comparatively smooth. While the setup steps of shell molding are more complex (and therefore more expensive) than casting methods like greensand, the overall process is often simplified, resulting in lower per-part costs.